Global change and river flow in Italy

The hydrological data of 23 flow gauges, evenly distributed across the Italian territory and covering almost 40% of it, have been analyzed in order to verify the occurrence of temporal trends and their rates of change. A total of 102 time series diagrams of the parameters considered, i.e. precipitation, runoff, maximum discharge, discharge exceed 10 days a year, were obtained. The results indicate that all the parameters considered show a decreasing trend. Also the comparison of bankfull discharge calculated for three periods, prior to 1951, 1951-1980 and 1981-2007, indicate a substantial decrease. The general decrease in river flow is accounted for in terms of global change (namely precipitation, land use change and water consumption increase). In the aim to summarize the pattern of change of the parameters considered, the data have been standardized and mean time series of Z score for a few representative rivers have been obtained. All these results depict for Italy a framework of substantial decrease of water resources (average precipitation and runoff decreasing rates are -2.11 and -2.65 mmyr-1, respectively) and sediment transport capacity with evident consequences on the river ecosystems and beach stability. The countertrending behavior of medium to high discharge of the Po River are analyzed and explained in terms of temperature increase. In order to investigate the role of the upstream catchment area in determining the variability of a few of the parameters considered in this study, simple regression analyses have been performed which demonstrate a high degree of accuracy in predicting specific discharges also for rivers without flow records or insufficient flow data.